Introduction to Freshwater Eels in Sri Lanka

Introduction to Freshwater Eels in Sri Lanka
Introduction to Freshwater Eels in Sri Lanka

Eel, (order Anguilliformes), any of more than 800 species of characterized by elongate wormlike forms. Anguilliformes hold the common freshwater eels as well as the voracious morays.

An eel is any ray-finned fish having a place with the order Anguilliformes, which comprises of eight suborders, 19 families, 111 genera, and around 800 species. Eels undergo significant improvement from the early larval stage to the particular adult stage. Most are active predators.

The expression “eel” is additionally used for some other eel-shaped fish, for example, electric eels (sort Electrophorus), spinny eels (family Mastacembelidae), and deep-sea spiny eels (family Notacanthidae). These different clades, be that as it may, developed their eel-like shapes separately from the genuine eels.

Eels are long fish, growing long from 5 cm (2.0 in) in the one-jawed eel (Monognathus ahlstromi) to 4 m (13 ft) in the slim mammoth moray. Adults go in weight from 30 g (1.1 oz) to well more than 25 kg (55 lb). They have no pelvic fins, and numerous species also lack pectoral fins. The dorsal and anal fins balances are twisted with the caudal fin, framing a single string running along a significant part of the length of the animal. Eels swim by producing body waves that venture to every part of their bodies. They can swim in reverse by turning around the heading of the wave.

Most eels live in the shallow waters of the sea and tunnel into the sand, mud, or among rocks. A larger number of eel species are nocturnal; they are seen living individually in holes, or “eel pits”. A few species of eels likewise live in more deep water on the continental shelves and over the slopes deep as 4,000 m (13,000 ft).members from Anguilla usually inhabit freshwater, however, they, as well, come back to the ocean to breed.

The heaviest true eel is the European conger. The most extreme size of this species has been estimated for as arriving at a length of 3 m (10 ft) and a load of 110 kg (240 lb). Other eels are longer, yet don’t weigh such a lot, for example, the thin goliath moray, which arrives at 4 m (13 ft).

Eels have an extraordinary life cycle. Definitely, it includes improvement and early development in the vast sea: the planktonic (free-drifting) dispersal of eggs and hatchlings, transformation, adolescent and grown-up development, and the movement of developing grown-ups to a fertile maritime region. Eels share the leptocephalus stage with a few different orders (Elopiformes [tarpons and relatives], Saccopharyngiformes [gulpers and relatives], and Albuliformes [bonefishes]). A prolarva, hatching from a generally large egg (up to 2.5 mm [about 0.1 inches] in breadth), quickly turns into a leaflike leptocephalus, which glides in the surface layers of the open sea for up to over two years before transforming. Despite the fact that the leptocephali were once thought to have been separated groups, their relationship with the Anguilliformes was before long recognized from transitional examples that proved larval and grown-up characters. They demonstrated so hard to acknowledge, in any case, that new larval sorts were named as species of the class Leptocephalus (however, they can’t really be viewed as various species from the grown-ups that produced them), representing the few hundred structures known. Leptocephali are normal in the upper 500 meters (approximately 1,600 feet) of the sea, an appropriation that might be related to the accessibility of food (diatoms and minute crustaceans). Their predators include different pelagic fishes. common eels, larval life is potentially four to a half year, yet some species may go through upward of a year as hatchlings. During this time, leptocephali, within sight of consistent flows, may generally scatter from the grown-up bringing forth region. Taking a shot at vast assortments of hatchlings from 1905 to 1930, a Danish scholar, Johannes Schmidt, set up the early life history of the European and American freshwater eels. Even though pieces of his work have been addressed, his depiction of a western Atlantic producing and a trans-Atlantic dispersal of leptocephali of these eels despite everything stands.

After arriving at full development, the hatchling starts a fast transformation wherein the body experiences a few dynamic changes. The body gets barrel-shaped and significantly diminished in mass, maybe by as much as 90% by weight, and the butt-centric vent propels from its subterminal situation to about the midpoint. The larval teeth are lost, the nose gets adjusted, the dorsal blade begins more distant forward, and the larval melanophores (dark color cells) vanish. Different changes, for example, the loss of the pectoral fins or a decrease of body length, may likewise happen.

Leptocephali are particularly not normal for their grown-ups, and the transformative changes are incredible to such an extent that a basic issue emerges in the connection of the extraordinary assortment of known leptocephali with their grown-ups. The transformation has been seen in aquariums and concluded in the seas from dynamic development arrangements in microscopic fish tests. Certain characters endure change and are significant in the acknowledgment of eel species. These incorporate the number of muscle sections (myomeres); the advancement of dorsal, butt-centric, and caudal balance beams; and the overall places of the renal vessels and the gallbladder. In numerous leptocephali, the larval melanophores likewise stay in the adolescent (or elver) stage.

The transformation includes physiological and social just as auxiliary changes, especially those identified with the presumption of a remote ocean, shallow-water, or freshwater method of life. Conversion is the system by which the leptocephalus, after a time of developing, taking care of, and contending with other comparably sorted out planktonic creatures, can enter exceptionally extraordinary natural surroundings where body shape, separated taking care of components, sense organs. Body coloration assumes a significant job in endurance. Transformation in all eels is most likely finished in the vast sea. The annual invasion of fresh-waters by Anguilla elvers is a locally well-known method; it happens during October–March in Europe and in spring in other warm regions.

eels are carnivores, taking care of differently on planktonic or benthic (base living) creatures. Development is reached after around ten years in the European freshwater eel (A. anguilla), however conceivably a lot before tropical marine species. The procedure of development and development has been most firmly concentrated in the European freshwater eel. In this species, both genders go through progressive periods of lack of bias, intelligent feminization, and adolescent hermaphroditism before getting conclusively male or female, the sex being resolved basically by natural variables.

Form And Function

An eel is recognized remotely from most different fishes by its lengthened body, which is only from time to time along the side compacted. A constant dorsal, anal, and caudal fin goes around the tail tip; pelvic fins are constantly missing, and gill openings are typically decreased. The body covering is normally scaleless. Minor takeoffs from this general body plan happen in the different eel families and are associated well with various methods of life. Ordinarily, a leptocephalus is stretch, along the side compacted, straightforward, and hardened, with noticeable W-molded myomeres and sharp forwardly coordinated larval teeth. At full development, eel hatchlings are 5 to 10 cm (approximately 2 to 4 inches) in length however might be a lot bigger, 45 cm (around 18 inches) on the statement of the snipe eel Nemichthys scolopaceus. Leptocephali are at any rate as various morphologically as their grown-ups: some are filamentous, while others are profound bodied

Pectoral and median fins are available in most leptocephali yet may disappear during transformation. Eyes are generally ordinary, however, they are once in a while adjustable, and the platform (a front beaklike projection) might be enormously reached out forward from the nose. The weaken viscera are situated along the ventral angle, beneath the myomeres. There is normally a straight unmodified digestive system, and the anal vent is frequently forward of the tail. In certain families, the larval gut is swollen or decorated at different focuses along its length, an adjustment of obscure importance. A long-lived, with an all-around defined gallbladder, happens anteriorly on either side of the digestive tract. The creating grown-up kidney lies at about mid-length. The organs are provided and depleted by numerous vertical veins, of which the last a couple is the biggest. The situation of the remainder of these vessels likens well with the division among the precaudal and caudal vertebrae and demonstrates the estimated position of the adult kidney.

In most leptocephali, melanophores happen anyplace on or in the body. These fluctuate from the moment and conservative to enormous and sporadically molded, frequently appropriated along the gut and horizontally in an assortment of examples.

In grown-ups, there is a solid propensity toward a decrease or loss of fins and a streamlining of the profile, at times additionally with a weakening of the body. The gill district is differently extended by back removal of the gill curves, joined by the partition of the pectoral support from the head. There are very much evolved pharyngeal tooth plates, and the pharynx has accepted a significant capacity in the development of nourishment into the throat. It likewise fills in as a successful siphon in the virtual nonappearance of suction by the gill covers (opercula) for the entry of the respiratory current. The opercular arrangement is abundantly diminished, albeit various bent branchiostegal rays (inside gill bolsters) are firmly evolved to help the long throat divider. Breath through the skin is significant in Anguilla and presumably likewise in different eels.

Sri Lanka is home to some of the amazing eel species found around the world. .mainly there are three main types of eels found in this island.

  1. True Freshwater eels
  2. Swamp eels
  3. Spiny eels

True Freshwater eels

A true eel is an elongated finned-fish belonging to the order Anguilliformes. There are more than 800 species of eel ranging in about 2 in (5 cm) to 13 ft (4 m) in length. The longest eel ever recorded was a slender giant moray eel captured in 1927—it measured 12.9 ft (3.9 m) long, or about the height of an elephant!

Although most eel species primarily live in saltwater, some eels travel between salt and freshwater environments to breed. For example, the European eel travels over 3,000 mi (4,800 km) from rivers in Europe to the Sargasso Sea to mate. Afterward, the adults die, while the young baby eels drift on Atlantic currents back to Europe—a journey that can take two to three years. Baby eels, called glass eels, are transparent and are sometimes harvested for food.

Sri Lanka is home to two species in Family Anguillidae know as the group of ray-finned fish that contains freshwater eels.

Mottled eel | Anguilla bengalensis

Introduction to Freshwater Eels in Sri Lanka

The mottled eel (Anguilla nebulosa), otherwise called the African mottled eel, the Indian longfin eel, the Indian mottled eel, the since a long time ago finned eel or the river eel, is a demersal, catadromous eel in the family Anguillidae. It was portrayed by John McClelland in 1844. It is a tropical, freshwater eel that is known from East Africa, Bangladesh, Andaman Islands, Mozambique, Malawi, Sri Lanka, Sumatra, and Indonesia and as of late from Madagascar. The eels spend through a large period of their lives in freshwater at a profundity scope of 3–10 meters, however, they move to the Indian Ocean to breed. males can arrive at a greatest complete length of 121 centimeters and a most extreme load of 7,000 grams. The eels feed mainly off of benthic scavengers, mollusks, finfish, and worms.

Because of its wide dissemination, the Mottled eel is recorded as Least Concern by the IUCN Redlist, they are trading in subsistence fisheries.

The specific characterization of the species was a discussion lately, where some significant fish sites (ex. Fish Base) ordered the species under the name A. nebulosa. In any case, as per the IUCN Red List 2015 adaptation, the fish species ought to be delegated A. bengalensis with some subspecies.

shortfin eel | Anguilla bicolor 

Introduction to Freshwater Eels in Sri Lanka

Anguilla bicolor is a type of eel in the variety Anguilla of the family Anguillidae, comprising of two subspecies.Anguilla Bicolor is additionally named shortfin eels, Bicolor eels are Catadromous; they have a similar normal in territory like the Anguilla-Anguilla and Anguillidae. Their gender organs are not created until they relocated to the ocean where they start to build up their sex organ and bringing forth in the remote ocean.The glass eel of Anguilla Bicolor seems to be indistinguishable like most different species; it is nearly unrealistic to distinguish them without DNA pairing during hatchlings and glass eels stage.

Introduction to Freshwater Eels in Sri Lanka

Swamp eels

The swamp eels (additionally stated “swamp-eels”) are a family (Synbranchidae) of freshwater eel-like fishes of the tropics and subtropics.Most species can inhale air and ordinarily live in bogs, lakes and clammy spots, some of the time covering themselves in the mud if the water source evaporates. They have different adjustments to suit this way of life; they are long and slim, they lack pectoral and pelvic fins, and their dorsal and anal fins are minimal. They lack scales and a swimbladder, and their gills open on the throat in a cut or pore. Oxygen can be ingested through the covering of the mouth and pharynx, which is wealthy in veins and goes about as a “lung”.

grown-up swamp eels have for all intents and purposes no fins, the hatchlings have enormous pectoral fins which they use to fan water over their bodies, in this manner guaranteeing gas trade before their grown-up breathing contraption creates. When about a fortnight old they shed these fins and expect the grown-up structure. Most types of swamp eel are bisexual, beginning life as females and later changing to male, however, a few eels start life as males and don’t change sex.

Lesser swamp eel | Monopterus desilvai

Introduction to Freshwater Eels in Sri Lanka

Monopterus desilvai (lesser bog eel) is an air-breathing type of fish in the family Synbranchidae. It is endemic to Sri Lanka. During propagation, the male watches and constructs a nest or tunnel. The particular name respects the Sri Lankan herpetologist Pilippu Hewa Don Hemasiri de Silva (b. 1927), who has been chief of the National Museums of Ceylon, in acknowledgment of the assistance and counsel he provided for Carl Gans when he was leading fieldwork in Sri Lanka.

Introduction to Freshwater Eels in Sri Lanka

Bengal swamp eel | Ophisternon bengalense

Ophisternon bengalense the Bengal eel, Bengal mudeel or onegill eel, is a type of fish in the family Synbranchidae. It is endemic to freshwater and saline water waterways and swamps in Oceania and South Asia. It is typically 100 cm in greatest length

Ophisternon bengalenseIntroduction to Freshwater Eels in Sri Lanka

Spiny eels

The name spiny eel is used to represent individuals from two unique families of fish: the freshwater Mastacembelidae of Asia and Africa, and the marine (and for the most part deep ocean) Notacanthidae. Both are so-named as a result of their eel-like shape and strong fin spines. These two families are not related: the Notacanthiformes have a place with the Superorder Elopimorpha, whose individuals are described by having leptocephalus hatchlings. The freshwater Mastacembelids don’t share this trademark and are mainstream examples in the aquarium exchange.Mastacembelid Spiny eels begin from three places. The Middle East, Southeast Asia, and Africa.In Africa alone, there are 43 species known from two genera: Aethiomastacembelus, with 19 known species, and Afromastacembelus, with 24 known species. Spiny Eels from Sri Lanka, China, Southeast Asia, and India are additionally from two genera: Macrognathus and Mastacembelus. The most normally discovered Spiny eels in the Aquarium exchange are the Macrognathus and Mastacembelus from Sri Lanka, China, Southeast Asia, and India. These incorporate such eels as the Peacock and Striped Peacock, the Tire Track or potentially White-spotted eel, the Zig Zag, Fire, Siamese, and Zebra eels.

Tire track eel | Mastacembelus armatus

The crisscross eel (Mastacembelus armatus), otherwise called the tire-track eel, tire-track spiny eel or marbled spiny eel, is a type of ray-finned, spiny eels having a place with the class Mastacembelus (Scopoli, 1777) of the family Mastacembelidae, and is local to the riverine fauna of India, Bangladesh, Pakistan, Sri Lanka, Thailand, VietNam, Indonesia and different pieces of southeast Asia. The species was portrayed as Macrognathus armatus by Lacepède in 1800. Other basic names for this famous aquarium species are panther spiny eel and white-spotted spiny eel. This species isn’t just a mainstream aquarium fish yet in addition as a food fish in its nations.


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Sri Lanka five-eyed spiny eel | Macrognathus aral


Macrognathus pentophthalmos, the Sri Lanka five-eyed spiny eel, is a little type of spiny eel that is endemic to freshwater environments in Sri Lanka. Depicted as a typical animal species as of late as 1980, for obscure reasons its populace quickly declined in the next years and there are no ongoing affirmed records. In 2012, it was recorded as “Fundamentally Endangered, perhaps “Extinct” in the Sri Lankan National Red List.

It is up to 19.5 cm (7.7 in) in standard length.Compared to Mastacembelus armatus, the main other spiny eels in Sri Lanka, M. pentophthalmos has a striped/plain (not mottled) design, and unmistakably isolated dorsal, caudal and anal fins. The English name of M. pentophthalmos alludes to the arrangement of dim spots on its dorsal fin.

Depicted as another species in 1854, it was then viewed as an equivalent word of the far-reaching M. aral. In 2008 it was indicated this was mixed up and M. pentophthalmos was restored as a legitimate animal group (the true M. aral isn’t found in Sri Lanka).



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